Stair climbing devices are suitable for the transport of devices, goods and persons and particularly of wheel chairs for moving the wheelchair together with a person sitting therein. The stair climbing device can be detachably mounted to such a wheelchair. However, stair climbing devices can also be fixedly integrated as a climbing unit in a wheel chair or another means of transportation for persons or goods. Examples for various embodiments of such stair climbing devices are for instance presented in DE 297 21 477 U1, DE 10 2004 043 778 A1 or WO 00/12371 A1.
Stairs constitute a considerable problem particularly for wheel chair drivers and people with impaired mobility. A stair climbing device as mentioned above, for example, provides the possibility that an assisting person can transport a wheel chair driver or a person with impaired mobility upstairs or downstairs without particular physical effort merely with the assistance of such a stair climbing device. In order to achieve this, such a stair climbing device can be detachably mounted to a wheel chair, provided that the stair climbing device is not designed as a part of the wheel chair as such. Together with the wheel chair the stair climbing device is driven to the first step of a flight of stairs. An assisting person tilts the stair climbing device together with the attached wheel chair towards his or her direction in a position of balance. When the ideal tilting position is reached, the assisting person only feels a minimum force in a forward or rear direction. When a climbing element of the stair climbing device gets in contact with the closest step in order to lift the stair climbing device on this next step, a load change reaction takes place which has to be compensated by the assisting person. The faster and stronger this load change reaction is, the stronger must be the reaction and corresponding compensation action of the assisting person.
In order to facilitate handling of such a stair climbing device, DE 199 12 932 C1 being a document of the generic kind suggests that the climbing unit of the stair climbing device is operated with varying propulsion speeds, wherein the propulsion speed shortly before contact of a climbing element on the next step is reduced as compared with a first predetermined propulsion speed so that a soft touchdown is achieved and after the touchdown on the next step the propulsion speed is increased again in order to effect the climbing action as a whole in a speedy manner. Due to the soft touchdown on the respective step, the handling of load change reactions by the assisting person is considerably facilitated. Furthermore, the climbing procedure is more gentle for the person sitting in the wheel chair.
In this known stair climbing device, the variation of the propulsion speed of the climbing element is carried out electronically by respective control of the drive motor. The drive motor is operated due to the electronic drive control during the climbing cycle with varying speed. This, however, leads to enhanced requirements regarding the electric drive motor.
In order to achieve the desired soft touchdown, the drive motor of the known stair climbing device presented in DE 199 12 932 C1 has to be operated with a rotational speed as low as possible directly prior to touchdown of the climbing element or a lifting element on a step as well as immediately thereafter in order to minimize the load change reaction as mentioned above and to insure a gentle touchdown. This means, however, that due to the start of the lifting action a sudden increase in force and a particularly high requirement of torque is given exactly when the electric driving motor is operating with a low rotational speed and exactly then, when the driving motor due to its design can deliver only a rather low torque. Such an electric motor therefore has to have particularly high torque reserves.